Proportional pneumatic solenoid valve

ABSTRACT

This three-way pneumatic solenoid valve comprises: a first inlet (1) connected to a first pressure source (A); a second inlet (2) connected to a second pressure source (D); an outlet (3) connected to a chamber at controlled pressure (C); a hollow body (4) into which t here emerges each of the paths so as to be set in communication therein in a selective fashion with at least one other path; and an electromagnet (5) secured to the body and including a core plunger (5a) capable of actuating means suitable for establishing the selective communication. 
     The latter essentially comprise a stationary valve (6) and a movable valve (7) housed in the hollow body, the stationary valve being capable of being open when the movable valve is closed and vice-versa, and these valves being defined by a shaft (60), a tubular and movable stopper member (67), and a sealed surface (70) actuated by the electromagnet. 
     This solenoid valve makes it possible to control the pressure in the chamber (C) as a function of the pressures of the first and second sources, in proportion to a control current signal from the electromagnet.

The present invention relates to a pneumatic solenoid valve comprising:at least two paths including a first inlet connected to a first pressuresource and an outlet connected to a chamber at controlled pressure; ahollow body into which there emerges each of the paths so as to be setin communication therein in a selective fashion, with at least one otherpath; and an electromagnet secured to the body and including a coreplunger capable of actuating means suitable for establishing saidselective communication a second inlet connected to a second pressuresource, the pressure of the first pressure source being relatively high,and the pressure of the second pressure source relatively low, and themeans suitable for establishing said selective communication comprise astationary valve and a movable valve housed in the hollow body, it beingpossible for the stationary valve to be open when the movable valve isclosed, and vice versa.

Insofar as such solenoid valves are capable of being used in brakingsystems, which are mass-produced and subject to very strictmanufacturing cost constraints, one object of the invention is topropose a solenoid valve making it possible to adjust the pressure inone chamber as a function of an electrical signal, and in which thestructure nevertheless remains sufficiently simple for manufacturing tobe easy and relatively inexpensive.

To this end, the solenoid valve of the invention is essentiallycharacterized in that the second inlet is located beyond the first inletwith respect to the outlet and in that the means suitable forestablishing said selective communication further comprise:

a shaft formed inside the hollow body along an axis in the extension ofthe outlet and carrying a first valve element of annular shape pointingtowards this outlet, extending in a plane which is substantiallyperpendicular to the axis, and intended to interact with a second valveelement so as to form, together with it, said stationary valve;

a third valve element formed at the periphery of a sealed surface andcapable of being displaced by the core plunger of the electromagnet,along the axis and towards the outlet, so as to interact with a fourthvalve element and to constitute with it said movable valve, this thirdvalve element extending in a plane which is distant from the stationaryvalve and substantially perpendicular to the axis, and;

a tubular and movable stopper member a first end of which carries saidsecond valve element and a second end of which carries said fourth valveelement, the second valve element being urged in the direction of thefirst valve element at least by a return spring towards a position forclosing the stationary valve in which the latter, the shaft, and thestopper member together prevent any communication between the firstinlet and the outlet whilst, in the absence of actuation of theelectromagnet allowing a communication between the second inlet and theoutlet through the movable valve and, with the third valve element urgedby actuation of the electromagnet, in the direction of the fourth valveelement into a position for closing the movable valve in which thelatter and the sealed surface prevent any communication between thesecond inlet and the outlet whilst allowing, at least for a minimumpredetermined actuation force of the electromagnet, a communicationbetween the first inlet and the outlet through the stationary valve,this stopper member in any position preventing any communication betweenthe two inlets.

Preferably, the tubular stopper member defines, together with the firstvalve element on the one hand, and with the third valve element on theother hand, substantially equal pressure-application surfaces and theoutlet as well as the electromagnet are located on said axis, whilst thetwo inlets emerge onto the periphery of the hollow body, at a distancefrom the axis.

According to a preferred embodiment, said sealed surface has a centralzone which is axially remote from the periphery of this surface in thedirection of the outlet, and forming a concavity pointing towards theelectromagnet; this sealed surface is then urged towards theelectromagnet by an elastic force acting on its periphery, and the coreplunger of the electromagnet acts on a first end of a push rod, a secondend of which bears on the inside of said concavity without relativealignment constraint.

Moreover, it is advantageous for the distance between the second and thefourth valve element to be variable so as to allow an intermediate stateof the solenoid valve in which the stationary and movable valves bothremain closed for a non-zero stroke of said core plunger. To this end,the tubular stopper member comprises, for example, first and secondtubular parts, which are substantially sealed with respect to eachother, sliding with respect to each other and with respect to saidhollow body, and respectively carrying the second and fourth valveelements.

In this case, the elastic force applied to the sealed surface may beexerted by a spring, tending to move the second tubular part of thestopper member and this sealed surface away from each other.

Finally, the core plunger may be guided in a stainless steel tube, whichoffers the advantage of reducing wear and the risks of the core plungerbecoming blocked, whilst exhibiting the property of being nonmagnetic.

Other features and advantages of the invention will emerge clearly fromthe description which is given hereafter, by way of an indication andwithout limitation, with reference to the appended drawings in which:

FIG. 1 is a sectional view of a solenoid valve in accordance with afirst embodiment of the invention; and

FIG. 2 is a partial sectional view of a solenoid valve in accordancewith a second embodiment of the invention.

The pneumatic solenoid valve of the invention includes three paths 1, 2and 3 and more precisely comprises, as shown in each of these figures:an essentially cylindrical hollow body 4 into which there emerges eachof the three paths so as be set in communication therein in a selectivefashion with at least one other path; a first inlet i constituting thefirst path, connected to a first pressure source, for example consistingof the atmosphere A; a second inlet 2 constituting the second path,connected to a second pressure source whose pressure is lower than thatof the first source and which, for example, consists of a vacuum sourceD; an outlet 3 constituting the third path, located beyond the firstinlet 1 with respect to the second inlet 2 and connected to a chamber atcontrolled pressure C; and an electromagnet 5 secured to the body andincluding a core plunger 5a capable of actuating means suitable forestablishing the selective communication between the three paths.

The means suitable for establishing the selective communication betweenthe three paths 1, 2 and 3 themselves comprise:

a stationary valve 6 and a movable valve 2 both housed in the hollowbody 1, the stationary valve being capable of being open when themovable valve is closed and vice-versa;

a shaft 60 formed inside the hollow body along an axis 8 in theextension of the outlet 3 and carrying a first valve element 6a ofannular shape pointing towards this outlet, extending in a plane whichis substantially perpendicular to the axis 8, and intended to interactwith a second valve element 6b so as to form, together with it, thestationary valve 6;

a third valve element 7a formed at the periphery of a sealed surface 70and capable of being moved by a rod such as 5b actuated by the coreplunger 5a of the electromagnet, along the axis 8 and towards the outlet3, so as to interact with a fourth valve element 7b and to constitute,together with it, the movable valve 7, this third valve element 7aextending in a plane which is remote from the stationary valve andsubstantially perpendicular to the axis 8, and;

a tubular and movable stopper member 67, a first end (to the left in thefigures) of which carries the second valve element 6b and a second end(to the right in the figures) of which carries the fourth valve element7b.

The second valve element 6b is urged in the direction of the first valveelement 6a, at least by a return spring 9, towards a position forclosing the stationary valve in which the latter, the shaft, and thestopper member together prevent any communication between the firstinlet 1 and the outlet 3 whilst allowing, in the absence of actuation ofthe electromagnet 5, a communication between the second inlet 2 and theoutlet 3 through the movable valve.

Moreover, the third valve element 7a is urged, by actuation of theelectromagnet, in the direction of the fourth valve element 7b into aposition for closing the movable valve 7 in which the latter and thesealed surface prevent any communication between the second inlet 2 andthe outlet 3 whilst allowing, at least for a predetermined minimumactuation force of the electromagnet, a communication between the firstinlet 1 and the outlet 3 through the stationary valve 6, the stoppermember 67 preventing, in any position, any communication between the twoinlets 1 and 2.

According to an advantageous feature of the invention, the tubularstopper member 67 defines, together with the first valve element 6a onthe one hand, and together with the third valve element 7a on the otherhand, pressure application surfaces of substantially equal areas.

Moreover, the outlet 3 and the electromagnet 5 are located on the axis8, whilst the two inlets 1 and 2 emerge onto the periphery of the hollowbody 4 at a distance from this axis 8.

According to the first embodiment of the invention (FIG. 1), the stoppermember 67 essentially consists of a flexible tube, for example made ofrubber, reinforced by a rigid tubular element 67a in the vicinity of itsfirst end (left-hand end), this tube, for example via its other end,being pressed in a sealed fashion against the inside of the hollow body4 between the first inlet 1 and the second one 2.

The sealed surface in this case assumes the shape of a disk 70, integralwith the rod 5b actuated by the core plunger 5a of the electromagnet,and the injection of electric current into this electromagnet thereforebrings about the displacement towards the left of the sealed surface 70,counter to the force exerted by a return spring 5c urging the coreplunger 5a and the rod 5b which is secured to it, towards a restposition (to the right in FIG. 1).

If, when the movable valve 7 is closed by this movement, the forcetransmitted to the electromagnet still allows the force of the springs5c and 9, to which is added the force exerted on the surface of themovable valve 7 by the pressure difference between the second inlet 2and the outlet 3 to be overcome, the sealed surface 70, which continuesto stop up the movable valve 7 is still further pushed towards the leftuntil the stationary valve 6 opens, which brings about the increase inpressure in the chamber C, for at least as long as this pressure doesnot reach atmospheric pressure, and the corresponding increase, untilthe surface 70 reaches an equilibrium position, of the force exerted onthis surface by the differential pressure counter to the actuation forceof the electromagnet.

Axial pins 10 evenly distributed about the axis 8 and allowing a passageof air are located on the inside of the hollow body 4 facing the stoppermember 67 so as to limit the crushing of the spring 9 and to limit thestroke of this stopper member.

According to a second embodiment of the invention (FIG. 2), the sealedsurface 70 has a central zone 70a which is axially remote from theperiphery of this surface in the direction of the outlet 3 and whichforms a concavity pointing towards the electromagnet 5.

This sealed surface is urged towards the electromagnet by a spring 11exerting an elastic force applied on its periphery, and the core plungerof the electromagnet pushes on a first free end 50a of a push rod 50, asecond free end 50b of which bears on the inside of the concavity of thesurface 70, each of these ends being free to pivot with respect to thecomponent against which it is pushed.

The rod 50, which is thus free of any relative alignment constraint, isguided in an axial bore 5c of the electromagnet, and this arrangementleads to a considerable reduction in friction and risks of blocking.

The second embodiment represented in FIG. 2 further makes it possible tocontrive easily that the distance between the second valve element 6band the force valve element 7b be variable, which allows an intermediatestate of the solenoid valve in which the stationary and movable valvesboth remain closed for a non-zero stroke R of the electromagnet coreplunger 5a, and gives the solenoid valve high operational stability.

To this end, for example, the stopper member 67 comprises first andsecond tubular parts 676 and 677, which are substantially sealed withrespect to each other, and slide with respect to each other and withrespect to the hollow body 4, and which respectively carry the secondand fourth valve elements 6b, 7b.

The second tubular part 677 supports the spring 11 which tends to moveit away from the sealed surface 70. Moreover, the parts 676, 677 of thestopper member are both pushed back elastically away from the outlet 3and towards the electromagnet by respective springs 12 and 13, a stop 14limiting the relative movement of these tubular parts 676 and 677.

Finally, as shown in FIG. 2, the core plunger is advantageously guidedin a thin stainless steel tube 15, making it possible to reduce frictionand wear.

According to another embodiment of the valve shown in FIG. 2, thenon-zero stroke R is increased in such a way that the second tubularpart 677 cannot push the first tubular part 676, the valve then workingas a pressure limiting valve.

We claim:
 1. A pneumatic solenoid valve comprising: at least two pathsincluding a first inlet connected to a first pressure source and anoutlet connected to a chamber at controlled pressure; a hollow body intowhich emerges each of the paths which communicate selectively with atleast one other path; and an electromagnet secured to the body andincluding a core plunger capable of actuating means suitable forestablishing said selective communication; and a second inlet connectedto a second pressure source,the pressure of the first pressure sourcebeing relatively high, and the pressure of the second pressure sourcerelatively low, and the means suitable for establishing said selectivecommunication comprising a stationary valve and a movable valve housedin the hollow body, the stationary valve being open when the movablevalve is closed, and vice-versa, characterized in that the second inletis located beyond the first inlet with respect to the outlet and in thatthe means suitable for establishing the selective communication furthercomprises: a shaft formed inside the hollow body along an axis in anextension of the outlet and carrying a first valve element of annularshape pointing towards the outlet, extending in a plane which issubstantially perpendicular to the axis and intended to interact with asecond valve element to form with the second valve element saidstationary valve; a third valve element formed at the periphery of asealed surface and capable of being displaced by the core plunger of theelectromagnet, along the axis and toward the outlet, so as to interactwith a fourth valve element and to constitute with the fourth valveelement said movable valve, the third valve element extending in a planewhich is distant from the stationary valve and substantiallyperpendicular to the axis, and; a tubular and movable stopper member afirst end of which carries said second valve element and a second end ofwhich carries said fourth valve element, the second valve element beingurged in the direction of the first valve element at least by a returnspring and toward a position for closing the stationary valve in whichthe stationary valve, the shaft, and the stopper member together preventany communication between the first inlet and the outlet while, in theabsence of actuation of the electromagnet, allowing a communicationbetween the second inlet and the outlet through the movable valve and,with the third valve element urged by actuation of the electromagnet, inthe direction of the fourth valve element, into a position for closingthe movable valve in which the movable valve and the sealed surfaceprevent any communication between the second inlet and the outlet whileallowing, at least for a minimum predetermined actuation force of theelectromagnet, a communication between the first inlet and the outletthrough the stationary valve, the stopper member in any positionpreventing any communication between the two inlets.
 2. The pneumaticsolenoid valve according to claim 1, characterized in that the tubularstopper member defines, together with the first valve element and withthe third valve element substantially equal pressure-applicationsurfaces.
 3. The pneumatic solenoid valve according to claim 2,characterized in that the outlet and said electromagnet are located onsaid axis, while the two inlets emerge onto the periphery of the hollowbody at a distance from the axis.
 4. The pneumatic solenoid valveaccording to claim 1, characterized in that said sealed surface has acentral zone which is axially remote from the periphery of the surfacein the direction of the outlet, and forming a concavity pointing towardsthe electromagnet, the sealed surface urged toward the electromagnet byan elastic force acting on a periphery thereof, and the core plunger ofthe electromagnet acting on a first end of a push rod a second end ofwhich bears on the inside of said concavity without relative alignmentconstraint.
 5. The pneumatic solenoid valve according to claim 1,characterized in that the distance between the second and the fourthvalve element is variable so as to allow an intermediate state of thesolenoid valve in which the stationary and movable valves both remainclosed for a non-zero stroke of said core plunger.
 6. The pneumaticsolenoid valve according to claim 5, characterized in that said tubularstopper member comprises first and second tubular parts which aresubstantially sealed with respect to each other, sliding with respect toeach other and with respect to said hollow body, and respectivelycarrying the second and fourth valve elements.
 7. The pneumatic solenoidvalve according to claim 5 or 6, characterized in that said elasticforce is exerted by a spring tending to move the second tubular part ofthe stopper member and said sealed surface away from each other.
 8. Thepneumatic solenoid valve according to claim 1, characterized in that thecore plunger is guided in a stainless steel tube.
 9. The pneumaticsolenoid valve according to claim 5 or 6, characterized in that saidnon-zero stroke is such that the second tubular part cannot move thefirst tubular part.